This invention relates to concrete form mouldings, and more particularly, to a concrete form mouldings formed from closed cell extruded polystyrene. The invention also encompasses an apparatus and method for manufacturing concrete form moulding strips from sheets of extruded polystyrene.
Concrete form mouldings are thin strips of material that can be built into concrete forms to give the resultant cast concrete a particular size, shape, or architectural feature. Such concrete form mouldings include chamfer, cant, rustication, reveal, drip, and cap strips.
Concrete form mouldings have commonly been made from various types of wood. Although the industry standard for years, these wooden concrete form mouldings had several drawbacks. First, the wooden moulding strips were bundled together in commercial packaging and these bundles were heavy and therefore difficult to handle and transport. Also, many types of wood were too porous and irregular for use as concrete form mouldings and the better, less permeable and more stable woods were expensive. Furthermore, wooden concrete form mouldings were expensive to machine into the required thin strips having a consistent cross-sectional shape, and even the best wooden concrete form moulding strips could warp or bow to the point of being unusable. The thin wooden concrete form moulding strips could also split as they were being attached to concrete forms.
Expanded bead polystyrene has also been used to form concrete form mouldings. Although the expanded bead polystyrene material was less expensive and overcame other problems associated with wooden concrete form mouldings, there were several problems with such concrete form mouldings which made them impractical. Perhaps the most important drawback to expanded bead polystyrene concrete form mouldings was that the material did not release easily from the moulded concrete once the concrete was set. The difficulty in releasing arose from the porosity and permeability of expanded bead polystyrene material. The material absorbed water and cement causing it to actually cement to the concrete as the concrete set. Traditional release agents could not be applied to the expanded bead polystyrene to alleviate the releasing problem because such release agents were petroleum based and dissolved the expanded polystyrene material.
Polystyrene concrete form mouldings have been manufactured from sheets or blocks of polystyrene material using hot wire cutting devices. The devices include an element known in the art as a harp having a series of a spaced-apart wires that are each as long as the length of moulding to be cut. The wires of harp are heated to a cutting temperature and then the harp is maneuvered through the sheet or block of polystyrene to cut the desired shape of moulding.
There were several problems with prior devices for forming concrete form mouldings from polystyrene or similar plastic materials. First, the machine for moving the harp relative to the plastic was very complicated and expensive. More importantly, it was difficult to maintain the proper tension in the long cutting wires required to cut the moulding strips lengthwise. When the wire loosened, it would bow as the harp moved through the plastic creating undesired curves or waves in the surfaces of the resultant moulding piece.